Dietary preference for methionine sources in weaned pigs

The objective of the current study was to investigate the preference of weaned pigs given the choice of diets supplemented with dl-methionine (DLM) or liquid dl-methionine hydroxy analog-free acid (MHA-FA). A basal diet (BD) was formulated to contain 2.5 g methionine (Met) per kilogram of diet. The experimental diets included: (1) BD, (2) BD + 1 g DLM/kg, (3) BD + 2 g DLM/kg, (4) BD + 1.13 g MHA-FA/kg, (5) BD + 1.52 g MHA-FA/kg, (6) BD + 2.25 g MHA-FA/kg and (7) BD + 3.05 g MHA-FA/kg. Sixty weaned mixed-sex pigs were allotted to 5 treatment groups with 12 pig replicates per treatment in a randomized complete block design. During a 35-day experimental period, pigs in treatment group 1 received the BD whereas pigs in the other 4 treatment groups were allowed to choose between a pair of diets with either added 1 g DLM/kg in combination with either 1.13 or 1.52 g MHA-FA/kg or 2 g DLM/kg in combination with 2.25 or 3.05 g MHA-FA/kg, respectively. Pigs were housed in individual pens and had free access to feed and water. Daily feed intake (FI) was used as an indicator of diet preference. Cumulatively, pigs showed a preference (% of total FI) for the diet added with 1 g/kg DLM at 74% (P<0.05) in group 2, and 65% in group 3. Irrespective of the level of MHA-FA supplementation (2.25 or 3.05 g/kg), a preference for the diet supplemented with 2 g DLM/kg was 84% (P<0.05) in groups 4 and 5. During the entire period, pigs consistently (P<0.05) consumed more and preferred the diets supplemented with DLM more than the diets supplemented with MHA-FA in groups 2, 4 and 5. The preference for diets supplemented with DLM was more pronounced at higher Met supplementation levels. Feeding pigs a pair of diets supplemented with DLM or MHA-FA improved (P<0.05) the final body weight, daily weight gain, and FCR. The performance of pigs among the Met-supplemented groups was not different. In conclusion, when given a choice pigs preferred the diets supplemented with DLM more than the diets supplemented with liquid MHA-FA.